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Does your podcasting or voiceover microphone hum? Do you hear a constant, low-pitched rumble, whine, or buzz in your audio tracks?

The problem might not be the microphone. The hum might exist in your room. The mic is just making it obvious.

I recently had a bad hum problem with a particular USB mic. I tried everything I could think of to make the noise go away:

changed USB cables

added a ferrite choke to the USB cable

changed USB ports on the computer

changed from desktop to laptop

turned off all the fluorescent lights in the house

unplugged and reset every connection in the audio chain

turned off the HVAC and every other appliance that might be causing line noise

None of these made any difference at all.

I tried a different USB mic. The hum was still there! It was less audible, but my spectrum analyzer showed a pronounced spike at 100Hz. Then I tried an analog mic through an external ADC. The 100Hz spike was still there. Clearly the hum was real — not a defective mic, not a bad cable, not some sort of weird USB crosstalk within the computer.

The problem was obvious, once I found it. For every test, I had mounted the mic to a boom arm attached to my desktop. (See my shootout and review of podcast/broadcast microphone boom arms.) Sitting on the same surface, three feet away, was a Seagate external USB disk drive, which runs 24×7 as a dedicated backup drive (running the OSX “Time Machine” utility). The vibrations from the spinning disk traveled across the desk, up the boom arm, and into the microphone. The mics without shockmounts, whether external or internal, captured more of the 100Hz hum.

I ran three tests at a fixed input gain level, using the USB mic most sensitive to hum. First up is the worst-case scenario, with the mic on its hard mount — essentially making it mechanically coupled to the disk drive’s motor. The 100Hz hum peaks at -44dB. (Click any of these images to zoom in.)

I replaced the mic’s hard mount with an elastic shockmount. The shockmount bought me 20dB of isolation; the hum dropped to -64dB.

Then I un-mounted the external Seagate drive from the desktop, and let its motor spin down. Predictably, the hum disappeared into the noise floor of the mic’s USB circuitry, around -100dB.

How to fix podcasting microphone hum

The lesson is that if your mic is picking up unwanted noise, the problem might not be some sort of esoteric EMI or RFI, or a bad mic or cable, but actual mechanical noise in your environment. Try this: take the mic off its desktop stand (USB mics nearly always come with desktop stands) and hold it it your hand. If that kills the hum, then there’s something on your desk that’s making the noise your mic is hearing. The culprit is probably the computer itself, or a disk drive, or a stereo component with a fan.

If you can’t get the noise source off the desk, you could try isolating it with Sorbothane feet or some other decoupling solution. I tested this idea by laying the Seagate external disk drive sideways on three Sorbothane feet; the 100Hz noise heard by the mic dropped by 30dB, well below the threshold of audibility. In other words, decoupling the disk drive from the desktop worked better at suppressing hum than putting the mic into a shockmount.

Another option is to mount the mic on a heavy floor stand. And I always recommend using a shockmount for the mic as well.

Bonus tip – freeware RTA

By the way, the RTA screenshots above are from BlueCat Software’s freeware FreqAnalyst spectrum analyzer plug-in. It is a great tool, and the price is right.

17 Responses to “How to fix microphone hum”

Great insight! It took me weeks to finally isolate an issue I was having. The culprit was my UPS (uninterruptible power supply). I moved all the audio gear to another leg of the fuse box and just kept the computer on the UPS. Problem solved.

Bill Poul

Dan Ortego

As usual, Matt finds a simple solution to a mysterious problem. Fortunately, that isn’t an issue I’ve encountered, or at least so far. My workstation is divided across three desk tables with anything that rumbles on the far end section.

One thing I can add to the mix, is to be mindful of backup power supplies and cheap surge protectors. In fact, I only use high-grade surge protection and no battery backup box. Components that have external power supplies can also be a source of noise even if you can’t hear them.

Susannah

Rodrigo

It happened to me as well. Fortunately, I have an old laptop and the vibrations were extremely obvious. Plus, it wasn’t a microphone but rather a portable Zoom H-1 recorder on a small tripod, so it was very obvious that the placement was the problem.

MikeCJ

I have a TLM 103 and 102. Just got a TLM 193. When I plug in the universal audio pre-amp and then motu interface, it hums. Hums even worse if you touch the wire mesh. The 102 and 103 are completely silent. I also checked a Shure SM58, quiet.

The only place it seemed to lose the hum was if it was within an inch of the interface. Again, the other mics, no hum anywhere. Any ideas?

Sunny

Finally I got the solution. I m staying on 7th floor and my mic stand is heavy steel based. I made my room as much sound proof as possible, but couldn’t get off the 100hz peak. Finally I took the mic in my hand and sat on bed. Voila the hum is gone. Seems the him was originating from ceiling fan of the 6th floor flat or probably from the vibrations of the whole apartment.

After reading your article, I figured out an incredibly simple fix for my bass hum issue. You know all those extra pairs of black socks you never wear? Well, I took 3 pairs and laid them into a square, crosshatch pattern. Then, I put my mic stand on top of it. Absolutely perfect vibration absorption. Thank you for helping me out! 🙂

Joan Sanaker

I have an audio technica ATR2500-USB microphone for doing voice over auditions. I just bought a portable sound booth with wonderful padding and a head cover for background noise. I have a hum in my recordings. I have turned off everything in the house, including the AC, except the refrigerator which is a couple of rooms away. I am stuck. What could be making the hum?

Thomas Johnson

I had a problem with both a periodic whining sound and thumping using a good quality microphone. After weeks or reading and trying numerous things, my solution was to wrap the microphone cord in lamp cord (silver and copper wires). This is the same cord used to wire speakers, back in the day. I did not have to wrap it tightly, just a gradual candy cane wrapping, secured with electrical tape to prevent unraveling. The key was that the headphones and mic cord pairing, that came boxed with my voice to text program, did not have the above disturbance when I used it to make a voice recording. I was never able to determine the source of the disturbance. But, now it does not matter. I truly hope this helps everyone dealing with the frustration I went through.